In the present application, the expression slurry is used as the general designation for a mixture of animal urine and excrements. Slurry can be divided into a solid, humid phase designated faecals in this application, and a liquid phase designated liquid manure in this application.
Liquid fertilizer is manufactured in the industry by suspending various nutrient salts in water. These salts have to be easily soluble in water, and they should typically contain nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulphur (S), magnesium (Mg), manganese (Mn), copper (Cu), boron (B), chlorine (Cl) or iron (Fe). The composition of these elements will typically be optimized in relation to the type of soil, the crops intended to be fertilized and the growth phase of the crops. These nutrient salts may, for example, be dosed in the form of a suitable combination of the salts: calcium nitrate (source of Ca and N), potassium phosphate (source of K and P), copper sulphate (source of Cu), manganese sulphate (source of Mn) and magnesium sulphate (source of Mg), boric acid (source of B), potassium chloride (source of K and Cl) and ferric citrate (source of Fe). This means that everybody with access to water and suitable water-soluble nutrient salts can combine and mix liquid fertilizer ready for use in the cultivation of arable land, forests, parks, golf courses, etc. Synthetically produced artificial fertilizer is a combination of nutrient salts, but the chemical properties of these nutrient salts do not depend on how they are produced. Therefore, the considerations behind the present invention are more or less to replace chemically produced artificial fertilizer with a product containing nutrient salts deriving from animals, which can be used as fertilizer.
It is well-known that slurry and/or faecals contain nutrient salts so that the slurry/the faecals can in themselves act as a fertilizer. Conventionally, the slurry has been applied directly without substantial treatment for fertilization of fields. However, the smell from a field sprayed with slurry is unpleasant and may be the subject of complaints from built-up areas close to the farm.
Methods for chemical treatment of slurry are known. An example of this is the addition of sulphuric acid, symbolized by H+ in the example below. This treatment is made to limit the evaporation of ammonia, symbolized by NH3 in the example below, from the slurry. Urea excreted in the liquid manure of mammals is degraded into ammonia in the slurry. This ammonia is claimed to inhibit the growth rate of mammals and to pollute the immediate animal house environment. When sulphuric acid is added to the slurry, the pH will drop and the ammonia will be transformed into ammonium ions according to the formula:
NH3 (dissolved in slurry phase)+H+→NH+4 (dissolved in slurry phase). The formation of ammonium ions, NH+4, thus inhibits the phase transition: NH3 (dissolved in slurry phase)→NH3 (dissolved in the house atmosphere), as the ammonium ion cannot evaporate. As shown by the example, the only purpose of the above method is to bind the ammonia to the slurry phase to limit the ammonia emission from the animal house. Actual processing into a commodity is not covered by the method. Moreover, the method relates to the entire slurry phase.
DK 134545 describes a method for producing a fertilizer product by treatment of animal dung with mineral acids and subsequent neutralization of the acid with a base. Preferably, sulphuric acid is used in the method, but nitric acid or phosphoric acid may also be used. However, the acid concentration used is moderate (pH is preferably around 1), and there is no obvious degradation or oxidation of the substrate, nor are any advantages of degrading or oxidizing the components of the animal dung described. The method is especially suitable for poultry fertilizer.
DD 134477 describes acid-catalyzed hydrolysis of animal dung for the winning of feedstuffs. The hydrolysis may be carried out by means of inorganic acids, and preferably concentrated hydrochloric acid is used. The process takes place at a temperature of approx. 100° C. After completed acid hydrolysis, the acid is neutralized with a base.
DE 301550 describes treatment of animal wastes with nitric acid followed by neutralization (with chalk) for the production of a product. The particular results of the treatment are not described in detail.
GB 1549959 describes a method for the production of a nutrient medium for micro-organisms through pressurized hydrolysis of slurry with mineral acids as a catalyst at an increased temperature. The hydrolysis is preferably carried out with sulphuric acid, and it is followed by neutralization with ammonium hydroxide.
It is not known that the synthetically produced nutrient salts normally supplied as artificial fertilizer may be produced directly at the animal producer's farm in connection with post-treatment of faecals and/or slurry from mammals.
Urease inhibition may be mentioned as another example of chemical treatment. Urease is an enzyme secreted with the faecals of mammals. Urease catalyzes the hydrolysis of the natural urea content in the liquid manure into ammonia. The method suggests processing of the liquid manure. Thus, the formation of, for example, the polymer urea formaldehyde through the addition of various reagents to a pre-treated fraction of the liquid manure is suggested for further export. It should be noted that the method does not comprise the faecals, but only the liquid manure.
The object of the present inventions is to supply the soil with nutrient salts from animal faecals in a suitable form that does not present odour nuisances to any notable extent. Another object of the invention is to provide a useful product that can be used as fertilizer on the lands belonging to the farm on which the slurry is produced or to make the product an object of trade. Yet another object is to render possible the production of a larger number of slaughter animals than is permitted by the authorities on the basis of the soil area available.